Your watch already measured the night. KnowSleep does the other half — it reads that night back to you as a paragraph, and once there are enough nights, as a report.
Download on the App StoreAn iPhone is enough; an Apple Watch adds detail · No account · Nothing leaves your device
The problem
48 minutes of deep sleep, 58 bpm, HRV 42 — your watch has had those numbers all along. Reading them a hundred times still won't tell you what to change. What's missing is the sentence: "because you were still drinking coffee at three yesterday afternoon."
Working that sentence out needs one thing a watch cannot measure: what you actually did. That is the only thing KnowSleep asks you for — and you can skip it.
How it works
The home screen has one main action: read last night. There is no form you have to fill in daily — read whichever night you like, as many times as you like.
Coffee, alcohol, a workout, stress, feeling unwell, a daytime nap, a change of routine, the phone in bed — tap whichever you remember. Caffeine and workouts can be read from Health, but they are shown beside the question as a reminder, never ticked for you.
The headline, what the record shows, what it means given what you told it, and one thing to watch tonight. There is also a 「basis」 page: which records were used, what you added, how many nights of history it looked at — and what it deliberately did not use.
Nothing to read on day one? A switch in Settings fills the whole app with a 45-night sample so you can see what it does. Not one of your own records is touched.
The point
Not "your sleep quality is below average" — anyone can say that. A sentence with your own numbers in it, and something you can go and change.
What matters more is when it declines to call one. A behaviour needs 4 nights with it and 4 nights without before it can be judged at all; anything that clears that bar then has to survive a correction for multiple comparisons (Šidák), so that one of eight behaviours isn't "significant" by luck. Short of that, it says so, and leaves it.
After enough nights
Weekly, monthly, quarterly, yearly. Not numbers stacked on a page — something you can read to the end: the stretch at a glance, what changed in it, which habits genuinely line up with your sleep, and what the next one will pick up.
"Still watching" is never quietly rendered as "no effect". It tells you how many nights are missing, and then stops talking.
Trends
No population ranking, no "you beat 68% of users". A single night bouncing around is normal; what matters is where your own line is heading.
Sleep score, bedtime, deep sleep, sleeping heart rate and HRV — over a week, a month, a quarter or a year, or any stretch of dates you pick yourself. All free; no window is locked.
It works without an Apple Watch too: the iPhone's own in-bed records carry the score, bedtime and time asleep. KnowSleep will not average watch nights together with phone-only nights — a figure built that way isn't real.
Privacy
KnowSleep has no server. Not "we promise not to misuse your data" — there is nowhere for it to go.
No sign-up, no email, no phone number. Install it and it works.
Every calculation happens on this iPhone. No sync, no cloud backup.
Reads sleep, heart rate, HRV, blood oxygen, respiration, wrist temperature and a dozen other types from Apple Health. One thing goes back: the coffee you tag, and only if you switch that on yourself. Full list
No ad SDKs, no analytics SDKs. Delete the app and the data goes with it — we hold no copy.
Price
Exactly one thing is behind the purchase: the weekly, monthly, quarterly and yearly reports. Everything else is free, with no cap on dates or repeats — every night's full data and charts, the sleep score, a reading for any day, and trends over every window.
The 7-day trial is provided by the App Store and starts when your subscription starts; cancelling within it costs nothing. Without subscribing you can read a complete sample report inside the app at any time — so you can see exactly what is on offer first. Prices shown are for the US App Store. Every other region has its own price, shown in your own currency before you pay.